High Altitude Operation - Honda WB 15 Owner's Manual

High altitude operation
At high altitude, the standard carburetor air-fuel mixture will be too
rich. Performance will decrease, and fuel consumption will increase. A
very rich mixture will also foul the spark plug and cause hard starting.
High altitude performance can be improved by specific modifications
to the carburetor. If you always operate your pump at altitudes above
6,000 feet (1,800 meters) have an authorized Honda water pump dealer
perform this carburetor modification.
If any case, engine horsepower will decrease about 3.5% for each
1,000 foot (300 meter) increase in altitude.
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When the carburetor has been modified for high altitude operation,
the air-fuel mixture will be too lean for low altitude use. Operation at
altitudes below 6,000 feet (1,800 meters) with a modified carburetor
may cause the engine to overheat and result in serious engine
damage. For use at low altitudes, have an authorized Honda water
pump dealer return the carburetor to original factory specifications.
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